Voltammetry of half-sandwich manganese group complexes of η6-PhC3B7H9 and η5-C60Bn2PhH2, two ligands that are cyclopentadienyl mimicks

Abstract The potentials of a series of one-electron oxidation and reduction reactions have been determined for manganese group half-sandwich complexes of the tricarbadecaboranyl ligand PhC 3 B 7 H 9 and the penta-organo fullerene ligand C 60 Bn 2 PhH 2 (Bn = benzyl). The anodic processes were studied in CH 2 Cl 2 and the cathodic processes were studied in both CH 2 Cl 2 and THF, the supporting electrolyte being [NBu 4 ][B(C 6 F 5 ) 4 ]. The manganese complex Mn(CO) 2 (PMe 3 )(PhC 3 B 7 H 9 ) ( 1 ) is a member of a three-electron transfer series which includes oxidation to 1 + (0.51 V versus ferrocene) and successive reductions to 1 − (−1.66 V) and 1 2− (−1.77 V). Both the oxidation and reduction of the closely-related complex Mn(CO) 2 (PPh 3 )(PhC 3 B 7 H 9 ) ( 2 ) are chemically irreversible under slow-scan cyclic voltammetry conditions. The rhenium complex Re(CO) 2 (PPh 3 )(PhC 3 B 7 H 9 ) ( 3 ) oxidizes ( E 1/2  = 0.82 V versus ferrocene) to a radical cation which, unlike its cyclopentadienyl analogue, shows no evidence of dimerization. Oxidation of the fullerene-based complex Re(CO) 3 (C 60 Bn 2 PhH 2 ) is more facile than that of its cyclopentadienyl analogue, in contrast to previous findings in this class of metal-fullerene derivatives. An electrochemical ligand factor, E L , of 0.63 is calculated for the PhC 3 B 7 H 9 ligand in manganese group half-sandwich complexes.